Psychological and pharmacological treatments for youth depression yield acute response and remission rates that are modest at best. In order to improve these outcomes, we developed and piloted a youth CBT intervention for insomnia, using R34 funding from NIMH, as an adjunct to traditional depression- focused treatment. This indirect route to improving depression outcomes is based on research indicating that the risk of depression is increased by insomnia, that sleep problems interfere with depression treatment success, and on emerging research on adult depression and insomnia from recent RCTs. Results from our youth pilot RCT showed promising depression and sleep outcomes. Therefore, we propose to conduct an adequately powered RCT (N=160) of our youth insomnia CBT intervention with depressed adolescents (ages 12 to 19) who have comorbid insomnia and have just initiated an incident course of treatment as usual (TAU) SSRI antidepressants (ADs). Qualified youth will be randomized to either: (a) insomnia-focused CBT (CBT-I) augmenting TAU antidepressants, or (b) a control condition of credible but minimally-effective sleep hygiene (SH) education augmenting TAU antidepressants. We will follow all youth for 12 months. We hypothesize that combined CBT-I+ADs will be superior for primary depression outcomes of response (CGI-I < 2) and major depressive disorder diagnostic remission, and primary sleep outcomes of actigraphy total sleep time and score on the Insomnia Severity Index. Secondary analyses will examine additional sleep and depression outcomes, and outcomes/mediation in two constructs relevant to the NIMH Research Domain Criteria (RDoC) initiative. Mediation analyses will examine whether improved sleep contributes to depression response-recovery. Moderation analyses will examine variation in intervention effect due to baseline age and gender, parent involvement, youth autonomy, and baseline sleep and depression severity. We will conduct economic analyses, aided by comprehensive healthcare-utilization data obtained via an integrated electronic medical record system. Should we find the predicted CBT-I benefits, cost-effectiveness results will be important for justifying next-step dissemination and implementation research. The launch of this study will be substantially expedited by the use of existing materials from our prior pilot study, including the CBT-I and SH treatment materials, and protocols. This application is responsive to priorities of the NIMH 2010 Council Workgroup Report on Interventions, in particular because of its use of personalized treatments based on individual differences; i.e., the presence of comorbid insomnia. Evidence on social/developmental and mental-health differences between youth and adults warrants a separate trial of CBT-I for youth insomnia and depression. In addition, the nature and impacts of insomnia are different for different ages, contributing to the importance of developing and testing adolescent-specific interventions for insomnia and depression.